Metallizable white opaque films are well known in the art, and are made for a variety of applications. For many applications, including but not limited to decorative packaging and certain label applications, it is highly desirable to achieve a brilliant, high gloss appearance from the metal layer. In prior art, opaque, metallized films employing an opacifying, void creating additive in the core in a sufficient quantity to achieve the desired opacity in the film, the metal layer tends to be somewhat dull; not having the high brilliance and gloss characteristics desired for many applications.
One way of achieving a greater brilliance or gloss in the metal layer is to avoid the use of void-creating additives, such as calcium carbonate, to achieve the desired opacity. Thus, for applications requiring a greater brilliance or gloss in the metal layer, opacity and whiteness can be achieved by incorporating TiO2 particles into the core of the film, which are too small to initiate voiding.
In addition, a non-voided metallizable skin composed of polypropylene, copolymers of polypropylene, or blends thereof, can be coextruded on one side of the core layer. Such a skin layer conceivably also could contain TiO2 to further improve the opacity and the whiteness of the film. While the use of non-voiding additives to establish whiteness and opacity in metallized films may provide satisfactory brilliance and gloss in the metal layer, they do not contribute to achieving other desired properties for label applications.
When the metallized film is intended to be used for label applications, and more specifically, for cut and stack label applications, it is highly desirable to employ aqueous cold glue adhesives on the label to adhere the label to the desired container. Several methods exist to permit the use of these cold glue adhesives in label applications. First, in paper labels, the cellulosic structure inherently is able to absorb excess moisture from the cold glue adhesive, thereby allowing adhesion of the paper label to the container. However, for many applications it is highly desirable to employ plastic labels, since they tend to be more durable than paper labels.
Plastic films are employed in the fabrication of labels that include an aqueous cold glue adhesive to adhere the label to a container, e.g., a glass or plastic bottle. For such applications, it is common practice to employ a secondary coating operation in which a hygroscopic coating is applied to a surface of the film, and this coating constitutes the adhesive-receiving layer. While these films are generally satisfactory for their intended purpose, they do require the use of a secondary coating operation, thereby increasing fabrication costs.
Exemplary disclosures of biaxially oriented metallized white film can be found in U.S. Pat. No. 5,425,996 (Wilkie et al.); U.S. Pat. No. 5,326,625 (Schuhmann et al.) and U.S. Pat. No. 4,883,698 (Bothe et al.).
U.S. Pat. No. 4,701,369, issued to Duncan, discloses an oriented multilayer film including a non-absorbent core that is free of voids and one or two surface layers. Each surface layer includes void creating additive to render the surface(s) absorbent to water. Duncan does not relate in any way to metallizable, or metallized films, and clearly does not relate in any way to a film designed to enhance the brilliance or gloss of a metallized film. However, Duncan does disclose a variety of void creating additives that are usable in this invention. The Duncan disclosure is hereby incorporated by reference herein.
In view of the above, there is a need for metallizable white opaque films that are capable of receiving a brilliant, high gloss metal layer thereon and that are well suited for use in label applications, and in particular cut and stack label applications wherein aqueous cold glue adhesives can be used, without the need for including any separate hygroscopic coating step. It is to such metallizable white opaque films, metallized films made therefrom, and labels made from the metallized films that the present invention relates.